Fully Kinetic Simulations of Driven Magnetic Reconnection With Boundary Conditions Relevant to MRX

Many simulations of magnetic reconnection use periodic boundary conditions which limit the physical relevance of the results when comparing with large open systems that occur in nature or with laboratory reconnection experiments. To address this issue, more realistic boundary conditions are employed to model the Magnetic Reconnection Experiment (MRX) using a fully kinetic, two-dimensional code. The simulation is made up of a box with conducting boundary conditions and two current-carrying wires. As the current is ramped down over the time scale of the simulation, a current sheet forms and elongates. Scaling comparisons for the length and width of the electron layer as well as the reconnection rate are presented. In both the experiment and simulation the thickness of the electron layer scales linearly with the electron skin depth when the plasma density is varied. However, in the experiment, the layer is four to five times thicker [1]. The period of the driving waveform is a key parameter that must be matched for these comparisons; the layer is typically longer and thinner when the drive is stronger. For strong drives, magnetic islands similar to previous undriven, open-boundary simulations [2] are sometimes observed in the present work but have not been conclusively identified in the experiment. Boundary conditions near the wires also play an important role; when a fraction of particles are reflected rather than lost, the elongation of the layer late in the simulation is limited. The simulation may also be used to study aspects of driven reconnection for which measurements are not currently available in the experiment. For example, the problem of energy transfer from fields to particles is investigated by measuring the ion and electron distribution functions within the layer. The results may inform future experimental studies of ion and electron acceleration. [1] Y. Ren, Princeton PhD Thesis (2007). [2] W. Daughton, et all., Phys. Plasmas. {13}, 072101 (2006).